GIBBS, JOSIAH WILLARD (1839-1903), American mathematical physicist, the fourth child and only son of Josiah Willard Gibbs (1790-1861), who was professor of sacred literature in Yale Divinity School from 1824 till his death, was born at New Haven on the 11th of February 1839. Entering Yale College in 1854 he graduated in 1858, and continuing his studies there was appointed tutor in 1863. He taught Latin in the first two years, and natural philosophy in the third. He then went to Europe, studying in Paris in 1866-1867, in Berlin in 1867 and in Heidelberg in 1868. Returning to New Haven in 1869, he was appointed professor of mathematical physics in Yale College in 1871, and held that position till his death, which occurred at New Haven on the 28th of April 1903. His first contributions to mathematical physics were two papers published in 1873 in the Transactions of the Connecticut Academy on "Graphical Methods in the Thermodynamics of Fluids," and "Method of Geometrical Representation of the Thermodynamic Properties of Substances by means of Surfaces." His next and most important publication was his famous paper "On the Equilibrium of Heterogeneous Substances" (in two parts, 1876 and 1878), which, it has been said, founded a new department of chemical science that is becoming comparable in importance to that created by Lavoisier. This work was translated into German by W. Ostwald (who styled its author the "founder of chemical energetics") in 1891 and into French by H. le Chatelier in 1899. In 1881 and 1884 he printed some notes on the elements of vector analysis for the use of his students; these were never formally published, but they formed the basis of a text-book on Vector Analysis which was published by his pupil, E. B. Wilson, in 1901. Between 1882 and 1889 a series of papers on certain points in the electromagnetic theory of light and its relation to the various elastic solid theories appeared in the American Journal of Science, and his last work, Elementary Principles in Statistical Mechanics, was issued in 1902. The name of Willard Gibbs, who was the most distinguished American mathematical physicist of his day, is especially associated with the "Phase Rule," of which some account will be found in the article Energetics. In 1901 the Copley medal of the Royal Society of London was awarded him as being "the first to apply the second law of thermodynamics to the exhaustive discussion of the relation between chemical, electrical and thermal energy and capacity for external work."

A biographical sketch will be found in his collected Scientific Papers (2 vols., 1906).